Conventionally, a hall element with using a semiconductor has generally has been used for detection of the magnetic field. But the detected minimum magnetic field strength of a two-dimensional electron-gas hall element with the best sensitivity is only approximately 10−3 Gauss. There is a superconducting quantum interference device (SQUID) as a magnetic field sensor with further better sensitivity than that of the hall element, and the SQUID can detect a magnetic field strength of 10−7 Gauss.
However, the SQUID has had various kinds of problems such as: (a) a problem that it can be used only in a low magnetic field area; (b) one that a magnetic shield is required; and (c) one that it is required to be operated at the liquid helium temperature.
Accordingly, the invention according to the application has been made, considering the above circumstances, and the object of the invention is to solve problems of the prior arts and to provide a high sensitive magnetic field sensor which can observe a little change of magnetic field in the high magnetic field area.